Progress has been made on the development of respiratory and flavivirus vaccines. Since a goal of this project is to develop a trivalent consisting of respiratory syncytial virus (RSV) subgroup A and B live virus vaccine components and a parainfluenza virus type 3 component, the status of studies with these vaccines will be described. None of these studies have been completed and the details will not be provided until the studies are complete. RSV subgroup A virus vaccine: Studies with recombinant RSV subgroup A viruses continue. The following viruses are in trials; rRSVA2cpts248/404delSH; (del SH = a virus with a deletion of the SH gene); rRSVA2cpts248/404/1030delSH; rRSVA2cpts530/1009delNS2; and rRSVA2cpdelNS2. RSV subgroup B virus vaccine: Studies with this subgroup have not been initiated. PIV3 virus vaccine candidates: Studies with the promising PIV3cp45 continue. The following studies are in progress: 1- A two dose infant trial examining the effect of interval between doses on vaccine take and immunogenicity; 2- A Phase II safety study; 3- A transmissibility study; 4- A study of the safety and immunogenicity of a combined live RSV and PIV3cp45 vaccine. A Phase I study with a live attenuated recombinant PIV3 vaccine in which the N gene of the human PIV3 virus has been replaced by the N gene of a bovine PIV3, a virus that is naturally attenuated for humans. Dengue 4 virus: Study of the safety and immunogenicity of the Dengue type 4 recombinant virus at doses less than 5 log10 are in progress.